1. Field of the Invention
This invention pertains to machines for exercising human muscles, and more particularly to isolation exercise machines that impose different loads on a exercising person during concentric and eccentric muscle functions.
2. Description of the Prior Art
Various types of exercise machines have been developed to exercise human muscles. In general, exercise machines fall into one of two broad groups: machines for exercising multiple pairs of muscles at one time, and machines that exercise only one pair of muscles at a time. The first broad group of machines is frequently referred to as compound machines. The second group is often referred to as isolation machines.
Regardless of whether one or several pairs of muscles are being exercised, the muscles can function in three different ways. The first is a positive or concentric function in which the muscles contract against a load that is less than the muscle strength. The second way is a static or isometric function in which the muscle attempts but is unable to contract against a load that is greater than the muscle strength. The third muscle function is a negative or eccentric function in which an external load is large enough to overcome the muscle strength and force the muscle to elongate in spite of an attempt by the person to contract the muscle.
Examples of prior compound exercise machines include those marketed by Powertec Direct Company of Milford, Pa. The Hammer Strength Company of Cincinnati, Ohio, and Promaxima Manufacturing Limited of Houston, Tex., also market respective lines of mechanical exercising equipment. None of the machines available from the foregoing companies is capable of increasing the load a person must resist during eccentric muscles functions compared with the concentric muscle functions.
Exemplary compound exercise machines are disclosed in my co-pending U.S. patent application Ser. No. 10/233,036 filed Sep. 30, 2002. The machines of that application include leverage arms that are pivoted to a frame. Weights of desired size are hung from the leverage arms. The exercising person pivots the leverage arm and lifts the weights during concentric muscle functions. A spotter applies a small additional force to the leverage arm during eccentric muscle functions. The small applied force imposes an additional load that the person must resist during the eccentric muscle function.
The three companies mentioned above also market isolation exercise machines. Typical prior isolation machines exercise the pectoral muscles, inner thighs, lateral deltoid muscles, posterior deltoid muscles, and latisimus dorsi muscles. The prior machines usually included a series of cables and cams that operated to raise and lower a weight during the exercise routines.
U.S. Pat. No. 5,125,881 shows an isolation exercise machine for exercising the rear deltoid muscles. The machine of that patent comprises two independently pivotable levers each having a weight and a counterweight. The levers are pivoted in response to pushing against the levers with the backs of a person's upper arms. U.S. Pat. No. 5,171,198 teaches an isolation machine having independently pivotable levers with weights and counterweights for exercising the lateral deltoid muscles.
Like the compound exercise machines presently available, the prior isolation exercise machines also impose the same load on an exercising person during both concentric and eccentric muscle functions. Thus, a need exists for an isolation exercise machine that takes full advantage of the capabilities of human muscles during eccentric functions.